Novel epoxy curing system

ABSTRACT

A novel epoxy resin curing agent comprises oligomeric poly(ethylenepiperazine). The resins comprise a vicinal polyepoxide and a curing amount of oligomeric poly(ethylenepiperazine).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to curable epoxy resins. More particularly, to anovel curing agent, oligomeric poly(ethylenepiperazine).

2. Prior Art

Epoxy resins constitute a broad class of polymeric materials having awide range of physical characteristics. The resins are characterized byepoxide groups which are cured by reaction with certain catalysts orcuring agents to provide cured epoxy resin compositions with certaindesirable properties. One such class of curing agents are generally theanhydrides. The most commonly used anhydride curing agents aredifunctional materials such as maleic anhydride, phthalic anhydride andthe like, as well as tetrafunctional materials such as pyromelliticdianhydride.

Epoxy resin formulations using prior art curing agents usually comprisetwo components, one containing the epoxy resin and the other containingthe curing agent. These must be mixed only when a cured product isdesired often by persons unfamiliar with formulating techniques.

A novel epoxy resin curing agent is disclosed herein which can be mixedwith the epoxy resin and stored as a one component system. This systemcan then be cured by the application of heat.

This novel curing agent also accelerates the cure of certain prior artcuring agents.

The cured epoxy resin compositions of the instant invention are usefulas coatings, castings, and sealants.

SUMMARY OF THE INVENTION

According to the broad aspect of the instant invention, an epoxy resinis cured with oligomeric poly-(ethylenepiperazine).

In one aspect, a curable epoxy resin composition comprises a vicinalpolyepoxide and a curing amount of oligomeric (polyethylenepiperazine).

In another aspect a curable epoxy resin comprises a vicinal polyepoxide,a curing amount of a prior art curing agent and oligomeric(polyethylenepiperazine).

DETAILED DESCRIPTION OF THE INVENTION

According to one embodiment of the instant inventive concept, blends ofa polyepoxide and oligomeric poly(ethylenepiperazine) are thoroughlyadmixed and cured in accordance with conventional methods to providecured epoxy resins having excellent properties.

Generally the vicinal polyepoxide containing compositions are organicmaterials having an average of at least 1.8 reactive 1,2-epoxy groupsper molecule. These polyepoxide materials can be monomeric or polymeric,saturated or unsaturated, aliphatic, cycloaliphatic, aromatic orheterocyclic, and may be substituted if desired with other substituentsbesides the epoxy groups, e.g., hydroxyl groups, ether radicals,aromatic halogen atoms and the like.

Preferred polyepoxides are those of glycidyl ethers prepared byepoxidizing the corresponding allyl ethers or reacting, by knownprocedures, a molar excess of epichlorohydrin and an aromaticpolyhydroxy compound, i.e., isopropylidene bisphenol, novolak,resorcinol, etc. The epoxy derivatives of methylene or isopropylidenebisphenols are especially preferred.

A widely used class of polyepoxides which are useful according to theinstant invention includes the resinous epoxy polyethers obtained byreacting an epihalohydrin, such as epichlorohydrin, and the like, witheither a polyhydric phenol or a polyhydric alcohol. An illustrative, butby no means exhaustive, listing of suitable dihydric phenols includes4,4'-isopropylidene bisphenol, 2,4'-dihydroxydiphenylethylmethane,3,3'-dihydroxydiphenyldiethylmethane,3,4'-dihydroxydiphenylmethylpropylmethane,2,3'-dihydroxydiphenylethylphenylmethane,4,4'-dihydroxydiphenylpropylphenylmethane,4,4'-dihydroxydiphenylbutylphenylmethane,2,2'-dihydroxydiphenylditolylmethane,4,4'-dihydroxydiphenyltolylmethylmethane and the like. Other polyhydricphenols which may also be co-reacted with an epihalohydrin to providethese epoxy polyethers are such compounds as resorcinol, hydroquinone,substituted hydroquinones, e.g., methylhydroquinone, and the like.

Among the polyhydric alcohols which can be co-reacted with anepihalohydrin to provide these resinous epoxy polyethers are suchcompounds as ethylene glycol, propylene glycols, butylene glycols,pentane diols, bis (4- hydroxycyclohexyl)dimethylmethane,1,4-dimethylolbenzene, glycerol, 1,2,6-hexanetriol, trimethylolpropane,mannitol, sorbitol, erythritol, pentaerythritol, their dimers, trimersand higher polymers, e.g., polyethylene glycols, polypropylene glycols,triglycerol, dipentaerythritol and the like, polyallyl alcohol,polyhydric thioethers, such as 2,2'-,3,3'-tetrahydroxydipropylsulfideand the like, mercapto alcohols such as monothioglycerol,dithioglycerol, and the like, polyhydric alcohol partial esters, such asmonostearin, pentaerythritol monoacetate, and the like, and halogenatedpolyhydric alcohols such as the monochlorohydrins of glycerol, sorbitol,pentaerythritol and the like.

Another class of polymeric polyepoxides which are in accordance with theinstant invention includes the epoxy novolak resins obtained byreacting, preferably in the presence of a basic catalyst, e.g., sodiumor potassium hydroxide, an epihalohydrin, such as epichlorohydrin, withthe resinous condensate of an aldehyde, e.g., formaldehyde, and either amonohydric phenol, e.g., phenol itself, or a polyhydric phenol. Furtherdetails concerning the nature and preparation of these epoxy novolakresins can be obtained in Lee, H. and Neville, K., Handbook of EpoxyResins, McGraw Hill Book Co., New York, 1967.

It will be appreciated by those skilled in the art that the polyepoxidecompositions which are useful according to the practice of the presentinvention are not limited to those containing the above describedpolyepoxides, but that these polyepoxides are to be considered merely asbeing representative of the class of polyepoxides as a whole.

The novel epoxy curing agent of this invention is oligomericpoly(ethylenepiperazine) which as the general formula ##STR1## where ncan be 1-20 but is preferably 2-6. It is a crystalline, hard, insolublesolid, readily reduced to a finely divided powder, melting at about 230°C. It is prepared by heating 1-(2-hydroxyethyl)piperazine in an inertliquid at an elevated temperature in presence of an acidic catalyst suchas an aromatic carboxylic acid.

This novel curing agent may be used alone or in combination with othercuring agent(s). Due to the highly insoluble nature of the oligomericpoly(ethylenepiperazine) in most liquids, including epoxy resins, itperforms as a latent catalyst, permitting formulation of one componentsystems. That is, the uncured epoxy resin and the oligomericpoly(ethylenepiperazine) may be mixed and stored until needed. At roomtemperature, no curing will take place. The mixture may then be appliedand heated, whereupon curing will take place. This offers manyadvantages including more accurate formulating and easier handling overthe two component systems of the prior art.

The oligomeric (polyethylenepiperazine) of the invention may also beused in a two component system where another curing agent is used. Whenused in combination with certain other curing agents, the oligomeric(polyethylene-piperazine) acts as an accelerator.

Derivatives of the poly(ethylenepiperazine) such as those prepared byreacting the oligomeric poly(ethylenepiperazine) with compounds whichreact with the terminal --OH and/or --NH groups are also useful ascuring agents in this invention. For example, carboxylic acids andalkylene oxides, to name only two, can be reacted to form derivatives ofoligomeric poly(ethylenepiperazine) which are useful as curing agents inthis invention.

The cured resins, in accordance with the instant invention, may beprepared in a conventional manner. The oligomericpoly(ethylenepiperazine) curing agent is admixed with the polyepoxidecomposition in amounts according to the functional equivalent weight ofthe curing agent employed. Generally the number of equivalents ofreactive groups is from about 0.8 to about 1.2 times the number ofepoxide equivalents present in the curable epoxy resin composition, withfrom 0.9 to a stoichiometric amount being preferred. The exact amount ofconstituents in accordance with the above general requirements willdepend primarily on the application for which the cured resin isintended.

The novel curing agent is incorporated into the resin by admixing. Theconstituents forming the curable material are intimately admixed bystandard methods and degassed in the presence of a commercial defoamerand minute amounts of silicone oils to prevent voids and bubbles.

In accordance with a preferred embodiment, a curable resin comprises adiglycidyl ether of 4,4'-isopropylidene bisphenol and an effectiveamount of the oligomeric poly(ethylenepiperazine) curing agent.According to a greatly preferred embodiment, from about 10 to about 30parts by weight of curing agent is used per 100 parts of resin.Generally, the mixture of epoxy resin and the oligomericpoly(ethylenepiperazine) is allowed to self-cure at elevatedtemperatures up to about 200° C.

It will further be realized that various conveniently employed additivescan be admixed with the polyepoxide containing composition of theinstant invention prior to final cure. For example, conventionalpigments, dyes, fillers, flame retarding agents and the like which arecompatible, natural or synthetic resins can be added.

Furthermore, known solvents for polyepoxide materials such as toluene,benzene, xylene, dioxane, ethylene glycol monomethylether and the likecan be used. The polyepoxide resins of the instant invention can be usedin any of the above applications for which polyepoxides are customarilyused.

The compositions of the instant invention can be used as impregnants,surface coatings, pottings, capsulating compositions and laminates.

The following examples illustrate the nature of the instant inventionbut are not intended to be limitative thereof.

EXPERIMENTAL Curing with Oligomeric Poly(Ethylenepiperazine)=E/P Polymer

This example demonstrates that satisfactorily cured epoxy resins areobtained using oligomeric poly(ethylenepiperazine) as the sole curingagent.

    __________________________________________________________________________                  A       B       C                                               __________________________________________________________________________    Formulation:                                                                  Epoxy resin (EEW 185)                                                                       100     100     100                                             E/P Polymer   15      20      25                                              Properties of cured 1/8"                                                      Casting:                                                                      Izod impact strength,                                                         ft.-lbs./in.  0.26    0.27    0.13                                            Tensile strength, psi.                                                                      7400    6000    5300                                            Tensile modulus, psi.                                                                       424000  434000  406000                                          Elongation at break, %                                                                      1.9     1.4     1.3                                             Flexural strength, psi.                                                                     13800   12500   11200                                           HDT, °C, 264 psi/66 psi.                                                             74/83   78/86   74.5/83                                         Shore D hardness, 0-10 sec.                                                                 88-86   89-87   89-87                                           __________________________________________________________________________     .sup.1 Cured 1 hr. 80°, 1 hr. 120°, 3 hrs 160° C.        Smaller amounts of E/P Polymer when used as a curative resulted in            incomplete curing.                                                       

We claim:
 1. An epoxy resin composition which comprises:a vicinalpolyepoxide having an average of at least 1.8 reactive, 1,2-epoxy groupsper molecule and an amount of oligomeric poly(ethylenepiperazine)effective for curing the epoxy resin.
 2. An epoxy resin composition asin claim 1 wherein the oligomeric poly(ethylenepiperazine) is present inan amount comprising at least 10 parts by weight per 100 parts by weightof epoxy resin.
 3. A method for curing an epoxy resin compositionwherein the epoxy resin comprises a vicinal polyepoxide having anepoxide equivalency of greater than 1.8 comprising the steps of:addingto said vicinal polyepoxide an effective amount of oligomericpoly(ethylenepiperazine) and heating the resulting mixture to effect acure.
 4. A method as in claim 3 wherein the oligomericpoly(ethylenepiperazine) is present in an amount comprising at least 10parts by weight per 100 parts by weight of epoxy resin.
 5. A curableresin composition comprising a diglycidyl ether of 4,4' -isopropylidenebisphenol polyepoxide and a curing amount of oligomeric(polyethylenepiperazine).
 6. A curable resin composition as in claim 7wherein the oligomeric poly(ethylenepiperazine) is present in an amountcomprising at least 10 parts by weight per 100 parts by weight ofpolyepoxide.